1. Field of the Invention
The present invention relates to a developing device, a developing cartridge, a process cartridge, and an image forming apparatus using these, which are applicable to an electrophotographic copying machine, printer or the like.
2. Description of the Related Art
Conventionally, an image forming apparatus using the electrophotographic image forming process adopts a process cartridge system, in which the image bearing member and the process means acting thereon are integrated into a cartridge, which is detachable with respect to the image forming apparatus main body. In this process cartridge system, the user can perform maintenance on the apparatus without relying on a serviceman, thus achieving a substantial improvement in terms of operability. As a result, this process cartridge system has come to be widely adopted in image forming apparatuses.
FIG. 17 shows an example of an image forming apparatus adopting this cartridge system, comprising an in-line type color printer 200 in which a plurality of process cartridges are arranged in a row. Regarding the developing means of process cartridges 207 (207a–207d) used in the image forming apparatus, two systems are generally known: a contact type development system in which development is performed with a developing roller 240 (240a–240d) being in contact with a photosensitive drum 201 (201a–201d) serving as the image bearing member, and a non-contact type development system in which development is performed with the developing roller being spaced apart from the photosensitive drum by a predetermined gap.
As an example of the developing device of a process cartridge, a developing device as shown in FIG. 18 has been proposed and put into practical use. The conventional developing device 207 shown in FIG. 18 has a developer container 245 containing a non-magnetic mono-component toner and equipped with a developing roller 240 serving as a developer carrying member, a developing blade 244 serving as a developer regulating member, and an application roller 243 serving as a developer applying member. The toner supplied to the developing roller 240 is conveyed to the portion where it abuts the developing blade 244 as the developing roller 240 rotates. Here, the toner on the developing roller 240 is turned into a uniform thin layer (toner coat) by the developing blade 244.
A developing bias is applied to the developing roller 240, and the toner on the developing roller 240 moves in correspondence with an electrostatic latent image formed on the photosensitive drum 201, visualizing a toner image on the photosensitive drum 201.
FIG. 19 is a longitudinal sectional view of the process cartridge. Here, the sectional view is taken along a plane passing the center of the developing roller 240.
As shown in FIG. 19, the developing roller 240 is rotatably mounted to bearing portions 247a and 248a of retaining members 247 and 248. Here, at one end of the developing roller 240, there is provided a regulating portion 240c for regulating the longitudinal moving amount of the developing roller 240. Further, mounted to the end surface on the opposite side is a helical gear 279 serving as a driving force transmission member for driving the developing roller. The torsional direction of the helical gear 279 is such that the thrust force generated when the driving force is applied to the developing roller 240 causes the developing roller 240 to move in the direction of the arrow C in the drawing.
Thus, in the state in which driving force is being applied to the developing roller 240, the developing roller 240 is constantly held at a fixed position by the thrust force of the helical gear and the regulating portion 240c, and it is possible to prevent image deficiency (so-called out of color registration generated when a number of colors are superimposed one upon the other) due to oscillation of the developing roller 240 in the thrust direction (the y-direction in the drawing).
However, in the conventional construction, it is necessary to provide play in the thrust direction of the developing roller 240 in order to absorb expansion and contraction of the developer container, etc., due to environmental fluctuation and the tolerance of each component. Thus, when no driving force is being applied to the developing roller 240, the developing roller 240 is movable in the thrust direction with respect to the developer container 245 and the developing blade 244.
Here, it is to be expected that during its transportation, the process cartridge suffers from vibrations in various directions. When it suffers from vibration in the longitudinal direction of the developing roller, it can happen that the developing roller 240 vibrates in the thrust direction within the process cartridge 207. At this time, the developing roller 240 and the developing blade 244 are rubbed against each other, with the result that the developing roller 240 undergoes deformation. Further, also when the developing roller 240 is moved by the thrust force generated by the helical gear 279, the developing roller 240 may suffer from a similar deformation.
Furthermore, the positional relationship between the point of contact 276 through which bias is supplied to the developing roller 240 and the developing roller 240 is not fixed. When a driving force is applied to the developing roller 240, the developing roller 240 moves to the regulating position due to the thrust force generated through meshing of the helical gear 279. However, the contact pressure immediately after the application of the driving force to the developing roller 240 is not fixed.